The present invention relates to a controlling method and an controlling apparatus each for positioning a robot during its point-to-point movement.
Generally, in positioning control for a robot between two points, speed control is performed by outputting a position instruction per a unit time (hereinafter referred to as the xe2x80x9cspeed instructionxe2x80x9d) based on a maximum speed and an acceleration that are set in advance, so that the robot is moved in accordance with the instruction.
This kind of speed instruction includes a linear speed instruction (trapezoidal speed instruction) as shown in FIG. 8a and a curved line speed instruction (S-shaped speed instruction) as shown in FIG. 8b, and the curved line speed instruction is often used in general because, with the linear speed instruction, a speed change is considerable at a point t1 or t2 in FIG. 8a. 
However, if a moving distance is short, residual vibration is generated immediately after stopping because a rising and falling of speed needs be steep, and an operation accompanying a large acceleration is performed even if the curved line speed instruction is used.
Laid-open Unexamined Japanese Patent Application No. 3-226805 discloses a method for controlling residual vibration after completing movement by altering a maximum speed and an acceleration that are set in advance to small values it a moving distance is short. More specifically, this method is for setting a maximum speed and an acceleration based on a ratio of a length of moving time in the case in which the moving distance is shorter than a standard distance with respect to a total of a length of time required for accelerating to a maximum speed set in advance and a length of time required for decelerating from the maximum speed to stop in a standard moving distance.
However, with this method, although an operation accompanying a large acceleration is not to be performed by making an acceleration low, there is a problem in that vibration peculiar to a robot is induced and residual vibration is generated after stopping operation if a speed wave form of a period synchronizing a vibration period peculiar to the robot is taken depending on a length of output time of a speed wave form because the vibration peculiar to the robot is not considered.
In addition, there is another problem in that, although the residual vibration immediately after completing a movement can be controlled if an acceleration is kept low, reduction in tact time for a moving operation cannot be achieved because a length of moving time from a start of movement until a completion of movement becomes longer.
Further, assuming that, although a frequency of residual vibration is a peculiar vibration frequency, for example, the residual vibration is generated at a frequency of 20 Hz when the robot is moved 25 mm. When the relationship between the moving time of the robot at the moment and the intensity of the residual vibration is as shown in FIG. 7, the residual vibration is made small if an acceleration for making the moving time of the robot 100 millisecond (hereinafter referred to as ms) is set. However, with the above-mentioned method, there is a problem in that, due to the nature of controlling the residual vibration after movement by slowing down the speed, the acceleration may be set such that the moving time is around 200 ms, and an optimal acceleration cannot be set.
Moreover, there is also a problem in that a lot of data must be set in advance such as an acceleration and a maximum speed for each moving distance, and a long measuring time is taken for determining the values.
The present invention has been devised to solve the above-mentioned problems, and it is an object of the present invention to provide a controlling method and a controlling apparatus both for positioning a robot that are capable of outputting an optimal speed instruction that can control a residual vibration after completing a moving operation, achieving reduction in tact time for the moving operation, and shortening the length of setting time.
A positioning controlling method of the present invention is a controlling method for positioning a robot for performing a point-to-point moving operation of the robot, which is characterized in that it measures a frequency of residual vibration of the robot that is stopped at a target position by performing a test operation in advance, and then measures a magnitude of residual vibration based on a frequency during each of different lengths of moving time for a fixed moving distance of the robot, thereby finding a relationship between the moving time and the vibration. The positioning controlling method is also characterized in that it calculates a shortest moving time at which the magnitude of the vibration is a minimum value in regard to said relationship, and controls a position of the robot during the calculated length of moving time.
The positioning controlling method is also characterized in that it controls a movement of the robot during the length of moving time calculated at the time of the test operation regardless of the moving distance.
The positioning controlling method is also characterized in that it controls the movement of the robot during the length of moving time calculated at the time of the test operation if the acceleration calculated from the above-mentioned relationship is within a maximum acceleration that is set in advance, and calculate a length of time that is a second shortest next to the shortest moving time at which the magnitude of the vibration is the smallest value, thereby to control the movement of the robot during said length of time.
The positioning controlling method is also characterized in that it measures a frequency of a residual vibration and, if a difference between the measured frequency value and a previously measured value is equal to or larger than an allowable value, calculates the length of moving time by performing the test operation.
According to the configuration mentioned above, the length of moving time can be found within a range in which the vibration frequency inherent to the robot is not induced and the maximum acceleration does not exceed that set in advance, and if the moving operation is controlled based on this length of moving time, the residual vibration after the completion of the moving operation can be controlled, reduction in tact time for the moving operation can be achieved, and the length of setting time can be shortened.
In addition, according to the configuration, since the moving time is simply found without depending on the moving distance, it is not necessary to calculate an optimal acceleration and a maximum speed for each moving distance, and the length of time required for determining parameters can be reduced.
In addition, a controlling apparatus for positioning a robot in accordance with the present invention is characterized by comprising: a measuring section for measuring a frequency of residual vibration of the robot that is stopped at a target position by performing a test operation in advance; and a control unit for measuring a magnitude of the residual vibration based on the frequency during each of different lengths of moving time for a fixed moving distance of the robot so as to find a relationship between the moving time and the magnitude of the vibration, calculating a shortest moving time at which the magnitude of the vibration is a minimum value in regard to said relationship, and moving the robot to the target position based on this moving time, thereby positioning the robot. The foregoing positioning controlling method of the present invention can be easily realized by using this positioning controlling apparatus.